A lubricant is the lubricating medium for the motor shaft to deal with the rotation of the bearing in an attempt to alleviate the abrasive loss therebetween. As such, how to make the most of the optimal lubricating effect of the lubricant and prevent the lubricant from leaking and draining are the two major subjects to overcome the abrasive loss out of operation.
In the past, the method against lubricant leakage is to add oil seal or washer on both sides of the bearing. However, such measure just delays the leakage. While the shaft is rotating at high speed, the lubricant subject to the centrifugal force resulting from the pump effect will form a thin lubricant film, which keeps spinning upwardly due to the rotation of the shaft, and deposits at the oil seal or the washer as a result of the blockage. In case of no proper guiding backflow channel, the deposited lubricant will be flung off at high speed to drain the lubricant. Consequently, instead of attaining a direct lubricant storage goal, such method can only temporarily get away with the drainage.
Accordingly, with reference to FIG. 1 of the Taiwan Patent Publication No. 456473 “Positioning structure of bearing and shaft tube”, the shaft tube 22 has a positioning hole 220 therein. A recess on the boundary of the positioning hole where corresponds to the bearing 20 is formed a lubricant storage space 222 such that, on the one hand, the centering shift of the bearing 20 can be avoided, and on the other hand, the additional lubricant storage space 222 is provided to store the lubricant so as to prevent it from leaking and draining.